1. Field Of The Invention
The subject invention generally relates to dock levelers, and more specifically, to dock levelers having a lip extension.
2. Description Of Related Art
Dock levelers are often used to compensate for a height difference that may exist between a loading dock platform and the bed of a truck parked at the dock. A dock leveler typically includes a ramp that is hinged at its back edge to raise or lower its front edge to generally match the height of the truck bed. Often an extension plate or lip is pivotally coupled to the ramp to bridge the gap between the ramp's front edge and a back edge of the truck bed. The ramp and lip provide a path for forklift trucks to travel from the loading dock platform and onto the truck bed, thus facilitating loading or unloading the truck.
For some dock levelers, the operating sequence involves pivoting the ramp upward to a height that allows the lip to pivot outward so it can extend over the back edge of the truck bed without striking it. The extended position of the lip can be latched to the ramp to allow the ramp enough time to descend and thus place the extended lip upon the truck bed. A contact force between the truck bed and the underside of the lip can be used to unlatch it, so when the truck departs, the unlatched lip is free to swing down.
An example of a latching-style dock leveler can be found in U.S. Pat. No. 3,997,932. It appears that a ramp pivots upward to its peak height, while the lip remains hanging downward in its pendant position. Then as the ramp pivots back down, a bar 23 forces linkages 14 and 17 to start lifting the lip. As the ramp continues downward, the lip continues to pivot outward and eventually latches as linkages 14 and 17 toggle over-center. The action of the lip engaging the bed of a truck unlatches the lip. When the truck departs, it appears that the lip falls freely. The resulting slamming action could be startling, unsafe, and possibly shorten the life of the dock leveler. Another problem exists when the ramp descends, but the lip misses the bed of the truck (e.g., no truck is present). It appears that the ramp would fully descend while leaving the lip extended. The next truck to arrive at the dock might back into the extended lip to damage both the truck and the dock leveler.
The '932, latching device is also incorporated in the dock levelers of U.S. Pat. Nos. 4,398,315 and 5,416,941. However, the '315 dock leveler adds a break-away coupling (FIGS. 3, 4 and 5) that buckles in the event that a truck backs into a lip that was left latched in an extended position. This might minimize damage to the truck and dock leveler in the event of a collision; however, it might be better to avoid the collision entirely. It appears that neither the '315 nor the '941 dock levelers address the problems associated with a lip being able to free-fall.
A latching dock leveler described in U.S. Pat. No. 4,091,488 addresses the free-fall problem, but in doing so introduces yet another problem. An additional link (item 54) is added to latch the lip. To unlatch the lip, link 54 needs to swing down away from item 58. It appears that the only force urging link 54 to swing down is its own weight. And that may be insufficient if link 54 were to seize on some dirt, corrosion, or otherwise bind where link 54 pivots on bracket 55 or possibly where link 54 engages item 58. Such binding could create all the problems normally associated with a lip left in its latched extended position after the truck departs.
Similarly, U.S. Pat. No. 3,995,342 also includes a separate additional link (item 32) to hold the lip in a latched state. Link 32 would appear to be susceptible to the forementioned problems of link 54 of the '488 device. Moreover, the '342 dock leveler also appears to allow its lip to fall freely without controlled descent.
Although some of the above-mentioned dock levelers have latching lips that are unlatched by the lip engaging the vehicle, the lip/vehicle engagement only triggers the unlatching motion as opposed to forcing it. Thus, additional mechanisms are needed, such as springs or weight, to provide the unlatching force.